The invention concerns a torsional vibration damper, especially for clutches that consists of a primary body and a secondary body.
Such a torsional vibration damper is e.g. described in EP 0 718 518 A1 which consists of a primary body and secondary body between which is located an arrangement of tangentially-acting spiral springs and tensioning bodies so that the primary body and secondary body can be rotated up to a maximum angle with a torsional characteristic determined by the spring arrangement. The tensioning bodies consist of cylinders and pistons that enclose a cavity which is filled with a cylindrical body of elastoplastic material whose diameter is less than the inner diameter of the cavity and is dimensioned so that it completely fills the cavity after the piston travels an initial, short path. The springs and the tensioning bodies serve as internal dampers to prevent rotary vibrations in the drive train excited by a drive.
DE 41 28 868 A1 describes a torsional vibration damper for similar clutches in which the primary body and the secondary body are only connected by tangentially active spiral springs. A friction ring is provided as the actual damping moment that becomes effective only after a certain angle of rotation is traversed between the primary and secondary bodies.
These prior art systems have the disadvantage that they only encompass part of the working spectrum of a drive but are ineffective in the additional load range. The problem is that the spring force and damping must correspond to the transmitted torque and speed for the load range while only a slight spring force and basically no damping are required to allow the clutch to be disengaged during idling. In the critical speed range, i.e., at speeds within the range the natural frequency, very strong damping is required since the angular acceleration would otherwise be too great in contrast to the primary side. This speed range is passed through primarily when the engine is started and when the load changes. In case of resonance, dynamic moment can arise that is a multiple of the nominal moment.
It is an object of the invention to present a torsional vibration damper especially for clutches where the damping characteristic can be optimally adapted.
For a solution, the invention suggests a torsional vibration damper consisting of a primary body and secondary body with a drag element that comprises at least one friction element with at least one pressure device, at least one catch and at least one elastic element.
The friction element can either interact with the primary body or the secondary body, and the catch drives the remaining body.
The pressure device is advantageously arranged so that a force acting on the pressure device increases the friction between the friction element and either the primary body or the secondary body. As will be explained in greater detail below, the pressure device can be formed by a friction ring edge or by an expanding ring that is situated in reference to the friction ring, and it interacts with the elastic element so that a force exerted by the elastic element on the pressure device, i.e., on the friction ring edge or the expanding ring increases the friction of the friction element with the primary or secondary body. Hence the friction caused by the friction element depends on the force exerted on the elastic element and hence on the angle of rotation between the primary and secondary bodies.
The arrangement according to the invention allows the damping characteristic to be suitably adapted, especially when large forces are exerted.
The elastic element advantageously has a rubber-like element in a cavity. The damping characteristic of the torsional vibration damper according to the invention can be advantageously influenced under large and small forces or angles of rotation. Under small forces or angles of rotation, the rubber-like element acts like an elastic spring. If the rubber-like element is further compressed until it fills the cavity, the elastic element consisting of the cavity and rubber-like element as if it enclosed a hydraulic liquid. In this state, the elastic element can counter substantially higher forces than prior-art torsional vibration dampers.
Particularly when the elastic element is tangentially compressed by a relative movement between the primary and secondary bodies, it is advantageous when the rubber-like element is without play in a tangential direction in the cavity. The elastic effect of the rubber-like element then begins immediately.
A particularly simple and hence reliable construction arises in this case when the cavity is delimited radially by a pressure device. The tangential compression of the rubber-like element determines its radial and axial expansion. The rubber-like element can act radially on the pressure device and hence increase the friction between the friction element and either the primary or secondary body. If there is also an axially-acting pressure device, it is also correspondingly acted upon by force.
The volume ratio of the cavity to the rubber-like element and their dimensions can adjust the behavior of the drag element depending on the angle of rotation between the primary and secondary bodies. It is possible in particular to select a rubber-like element that radially fills the cavity at a few sites when relaxed. Upon axial compression of the rubber-like element, slight, direct force is transmitted to the radial pressure device. Likewise, the rubber-like element can be axially designed to exert a selected force on an axial pressure device.
Of course the cavity does not have to be fully enclosed. It is sufficient for the elastic element or rubber-like element to be securely held, or for the edge of the cavity to hold the rubber-like element in the cavity so that the elastic element cannot be excessively pressed out of the cavity.
The force on the rubber-like element can result from a reduction in volume of the cavity due to a relative rotational movement between the primary and secondary bodies. In particular, it is advantageous when the reduction in volume is tangential since such a movement corresponds to the relative movement between the primary and secondary bodies, and the force does not have to be diverted. In particular, axial force is avoided between the primary and secondary bodies.
Independent of this, the torsional vibration damper consisting of a primary body and secondary body can include a drag element that has at least one friction element with at least one essentially tangential stop, at least one essentially tangential catch and at least one elastic element that acts tangentially between the stop and catch, whereby the friction element either interacts with the primary or secondary body, and the catch drives the other cited body.
The tangentially-acting arrangement of the elastic element between the stop of the friction element and the catch allow an optimum adaptation of the damping characteristic, i.e., the rotational characteristic caused by the friction element even when the angle of rotation between the primary and secondary bodies is very small. In particular, the noise that arises in clutches upon load changes when idling caused by very small forces can be more effectively avoided in this manner in contrast to prior art clutches.
The pressure device can be designed so that it acts radially. This has the advantage that the force that acts radially on the pressure device is captured by the torsional vibration damper, and no axial force acts on the other components such as the clutch. This advantage can be attained by using a friction element with a friction surface which has a surface component that extends radially outward.
To attain a minimum friction between the friction element and the primary or secondary body even when the pressure device is not acted on by the elastic element, the friction element can be a pretensioned spring. In particular, this increases adaptability in the low load range.
Of course it does not matter in the cited arrangements whether the catch drives the primary or secondary bodies or whether the friction element takes energy from the system by rubbing on the secondary or primary body.
It is preferable for there to be an elastic element on both sides of the catch in a tangential direction, and tangential stops abut the elastic elements or visa versa. The advantages of the present invention can be exploited independent of the rotational direction between the primary and secondary bodies.
The ring element is annular in one simple embodiment and designed as a drag ring. A catch ring can be correspondingly provided that has one or more catches. The catches or catch ring can have holes in which protrusions engage that are on the primary or secondary bodies. This is a simple mechanism to create a drive connection between the catches or catch ring and the corresponding body. Of course, other connections can be provided between the catches and corresponding primary or secondary bodies for a drive connection. In particular, the catch or catch ring can be provided with projections that engage in the recesses of the corresponding body.
In particular, when a drag ring is used as the drag element, it is advantageous to use a friction ring as the friction element. As stated above, the axial force can be reduced that acts on the other components (such as the clutch) by a friction surface with radially-projecting surface components. Such surfaces can e.g. be realized by a friction ring with an essentially L-shaped cross-section with a leg facing radially outward, or by a friction ring with an essentially U-shaped cross-section that is open in an axial direction. This friction ring should rotate in a corresponding recess, e.g. a U-shaped groove and rub against the corresponding body.
When a friction ring with an essentially L-shaped cross section is used, the processed surface in the corresponding body can be minimized, and one only has to correspondingly process the area of the body that contacts the friction surface, while the rest can remain an unprocessed cast part.
To make it easier to radially displace the radial friction surfaces by the force exerted on the pressure device, at least one axial slot can be provided in the corresponding surface.
The friction ring can be used to form the cavity for the rubber-elastic element, e.g., when it has a U-shaped cross-section and its open side is suitably closed e.g. by the catch ring. This makes it rather difficult to process the friction ring, however, and a suitable cavity is very difficult to realize when an L-shaped friction ring is used. In addition to the friction ring, the friction element can comprise an expanding ring that has at least one stop and is essentially U-shaped and open in an axial direction. The expanding ring is covered by the catch ring to form the essentially sealed cavity. The expanding ring is placed on the friction ring so that when the expanding ring expands or is displaced, the friction of the friction ring on the primary or secondary body is increased. Such an expanding ring makes it easy to use an L-shaped friction ring.
When an expanding ring is used, the torsional vibration damper can be easily pretensioned by cutting the expanding ring at one place and inserting a tangentially-acting pretension spring in the cut. If this expanding ring is inserted in the corresponding friction ring, the tangentially-acting pretension spring radially expands the expanding ring, i.e., radially enlarges the expanding ring diameter. This brings about pretension that is evenly distributed over the perimeter of the friction ring.
The torsional vibration damper can have an additional catch that interacts with a stop upon a certain angle of rotation. The characteristic of the drag element can hence be adapted to a large range of specific requirements. In particular, it is possible to design the catch and the stop so that they are basically rigid in relation to each other. With this arrangement, the drag element is entrained by the additional catches starting at a specific angle of rotation so that the elastic element is no longer compressed. With such an arrangement, the characteristic of the drag element remains constant starting at a specific angle of rotation.
Depending on the requirements, the additional catch and the stop can be elastic in relation to each other. With this arrangement, it is advantageous when an elastic element is between the additional catch and the stop. In this manner, the characteristic of the drag element is determined by two elastic elements starting at a specific angle of rotation.
Of course, the presence of an elastic element between a catch on one of the bodies and a stop of a drag element can be advantageously used independent of the other features of the torsional vibration damper. The same holds true for the presence of another catch that interacts with a stop upon a certain angle of rotation. The latter arrangement can ensure that the drag element is suddenly entrained starting at a specific angle of rotation with the catch and hence with one of the two bodies.
The present invention can be advantageously used especially for torsional vibration dampers where the primary and secondary bodies can only be rotated against each other by a specific angle of rotation due to the dimensions of the torsional vibration damper. Such dimensions can e.g. be realized when the primary and secondary bodies engage with a certain amount of play, or when there are wedges that prevent turning after a certain angle of rotation.